<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tomcat 7 Architecture (7.0.42) - Architecture Overview</title><meta name="author" content="Yoav Shapira"><style type="text/css" media="print">
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        </style></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img src="../images/tomcat.gif" align="right" alt="
      The Apache Tomcat Servlet/JSP Container
    " border="0"></a></td><td><h1><font face="arial,helvetica,sanserif">Apache Tomcat 7</font></h1><font face="arial,helvetica,sanserif">Version 7.0.42, Jul 2 2013</font></td><td><!--APACHE LOGO--><a href="http://www.apache.org/"><img src="../images/asf-logo.gif" align="right" alt="Apache Logo" border="0"></a></td></tr></table><table border="0" width="100%" cellspacing="4"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr noshade size="1"></td></tr><tr><!--LEFT SIDE NAVIGATION--><td width="20%" valign="top" nowrap class="noPrint"><p><strong>Links</strong></p><ul><li><a href="../index.html">Docs Home</a></li><li><a href="index.html">Architecture Home</a></li><li><a href="http://wiki.apache.org/tomcat/FAQ">FAQ</a></li><li><a href="#comments_section">User Comments</a></li></ul><p><strong>Contents</strong></p><ul><li><a href="index.html">Contents</a></li><li><a href="overview.html">Overview</a></li><li><a href="startup.html">Server Startup</a></li><li><a href="requestProcess.html">Request Process</a></li></ul></td><!--RIGHT SIDE MAIN BODY--><td width="80%" valign="top" align="left" id="mainBody"><h1>Architecture Overview</h1><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Overview"><strong>Overview</strong></a></font></td></tr><tr><td><blockquote>
<p>
This page provides an overview of the Tomcat server architecture.
</p>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Terms"><strong>Terms</strong></a></font></td></tr><tr><td><blockquote>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Server"><strong>Server</strong></a></font></td></tr><tr><td><blockquote>
<p>
In the Tomcat world, a
<a href="../config/server.html">Server</a> represents the whole container.
Tomcat provides a default implementation of the
<a href="../api/org/apache/catalina/Server.html">Server interface</a>
which is rarely customized by users.
</p>
</blockquote></td></tr></table>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Service"><strong>Service</strong></a></font></td></tr><tr><td><blockquote>
<p>
A <a href="../config/service.html">Service</a> is an intermediate component
which lives inside a Server and ties one or more Connectors to exactly one
Engine.  The Service element is rarely customized by users, as the default
implementation is simple and sufficient:
<a href="../api/org/apache/catalina/Service.html">Service interface</a>.
</p>
</blockquote></td></tr></table>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Engine"><strong>Engine</strong></a></font></td></tr><tr><td><blockquote>
<p>
An
<a href="../config/engine.html">Engine</a> represents request processing
pipeline for a specific Service.  As a Service may have multiple Connectors,
the Engine receives and processes all requests from these connectors, handing
the response back to the appropriate connector for transmission to the client.
The <a href="../api/org/apache/catalina/Engine.html">Engine interface</a>
may be implemented to supply custom Engines, though this is uncommon.
</p>
<p>
Note that the Engine may be used for Tomcat server clustering via the
jvmRoute parameter.  Read the Clustering documentation for more information.
</p>
</blockquote></td></tr></table>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Host"><strong>Host</strong></a></font></td></tr><tr><td><blockquote>
<p>
A <a href="../config/host.html">Host</a> is an association of a network name,
e.g. www.yourcompany.com, to the Tomcat server.  An Engine may contain
multiple hosts, and the Host element also supports network aliases such as
yourcompany.com and abc.yourcompany.com.  Users rarely create custom
<a href="../api/org/apache/catalina/Host.html">Hosts</a>
because the
<a href="../api/org/apache/catalina/core/StandardHost.html">StandardHost
implementation</a> provides significant additional functionality.
</p>
</blockquote></td></tr></table>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Connector"><strong>Connector</strong></a></font></td></tr><tr><td><blockquote>
<p>
A Connector handles communications with the client.  There are multiple
connectors available with Tomcat. These include the
<a href="../config/http.html">HTTP connector</a> which is used for
most HTTP traffic, especially when running Tomcat as a standalone server,
and the <a href="../config/ajp.html">AJP connector</a> which implements
the AJP procotol used when connecting Tomcat to a web server such as
Apache HTTPD server. Creating a customized connector is a significant
effort.
</p>
</blockquote></td></tr></table>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Context"><strong>Context</strong></a></font></td></tr><tr><td><blockquote>
<p>
A
<a href="../config/context.html">Context</a>
represents a web application.  A Host may contain multiple
contexts, each with a unique path.  The
<a href="../api/org/apache/catalina/Context.html">Context
interface</a> may be implemented to create custom Contexts, but
this is rarely the case because the
<a href="../api/org/apache/catalina/core/StandardContext.html">
StandardContext</a> provides significant additional functionality.
</p>
</blockquote></td></tr></table>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Comments"><strong>Comments</strong></a></font></td></tr><tr><td><blockquote>
<p>
Tomcat is designed to be a fast and efficient implementation of the
Servlet Specification.  Tomcat came about as the reference implementation
of this specification, and has remained rigorous in adhering to the
specification.  At the same time, significant attention has been paid
to Tomcat's performance and it is now on par with other servlet containers,
including commercial ones.
</p>
<p>
In recent releases of Tomcat, mostly starting with Tomcat 5,
we have begun efforts to make more aspects of Tomcat manageable via
JMX.  In addition, the Manager and Admin webapps have been greatly
enhanced and improved.  Manageability is a primary area of concern
for us as the product matures and the specification becomes more
stable.
</p>
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